Method for producing SiGe-based zones at different concentrations of Ge

Abstract

A method for forming SiGe-based regions with different Ge concentrations is provided. After defining the regions 1, 2 on a SOI substrate, a grating of masking patterns is formed on at least one region 2 . After the epitaxial growth of a Ge-based layer in each of the regions, a first vertical diffusion is carried out. A second horizontal diffusion is then carried out such that the Ge diffuses beneath the masking patterns of the region 2 . Thus, the region 2 has a Ge concentration that is lower than the Ge concentration of the region 1.

The invention claimed is: 
     
       1. A method for forming at least two SiGe-based regions in a silicon-based layer, comprising steps of:
 providing a substrate comprising the silicon-based layer; 
 defining at least a first enrichment region by exposing a first portion of the silicon-based layer; 
 forming, by epitaxial growth, a first Ge-based layer with an initial Ge concentration [Ge] 0  on the first portion, at the first enrichment region; 
 diffusing, during a first diffusion by oxygen annealing, in a first direction z perpendicular to the first Ge-based layer, germanium of the first Ge-based layer in the first portion corresponding to the first enrichment region, the first portion thus becoming a first SiGe-based portion having a first Ge concentration [Ge] 1 , and the first Ge-based layer thus becoming a first oxide layer; 
 defining at least a second enrichment region where the silicon-based layer is exposed, the at least one second enrichment region being separate from the first enrichment region; 
 forming a grating of masking patterns on the exposed silicon-based layer within the at least one second enrichment region, so as to define a plurality of transient portions of the silicon-based layer; 
 forming, by epitaxial growth, a second Ge-based layer with the initial Ge concentration [Ge] 0  on the transient portions of the silicon-based layer, at the second enrichment region; 
 diffusing, by oxygen annealing, in the first direction z, germanium of the second Ge-based layer into the transient portions, such that the transient portions become SiGe-based transient portions each having the first Ge concentration [Ge] 1 ; and 
 after the diffusing of the germanium by oxygen annealing in the first direction z, diffusing, during a second diffusion, in a second direction x parallel to the silicon-based layer, the germanium of the SiGe-based transient portions within the silicon-based layer, beneath the grating of masking patterns, so as to form at least a second SiGe-based portion having a second Ge concentration [Ge] 2  that is lower than [Ge] 1 , at the second enrichment region. 
 
     
     
       2. The method according to  claim 1 , wherein the first and the second SiGe-based portions are formed simultaneously. 
     
     
       3. The method according to  claim 1 , wherein the grating of masking patterns is formed such that the grating has an aperture density D between 0 and 1, 0<D<1, and the second Ge concentration [Ge] 2  is proportional to the aperture density D such that [Ge] 2 =D·[Ge] 1 . 
     
     
       4. The method according to  claim 1 , wherein the grating of masking patterns comprises masking patterns with a characteristic masking dimension Lm i , spaced apart from one another by a grating period Lo i , such that 10>Lo i /Lm i >2. 
     
     
       5. The method according to  claim 4 , wherein the characteristic masking dimension Lm i  is selected such that Lm i  is less than twice a diffusion distance d of the germanium within the silicon-based layer in the second direction x, during the second diffusion. 
     
     
       6. The method according to  claim 4 , wherein the masking patterns are in the form of parallel lines, square or rectangular pads, or a gate. 
     
     
       7. The method according to  claim 1 , wherein the first and the second Ge-based layers are formed by one and the same epitaxial growth, such that the first and the second Ge-based layers have a same initial Ge concentration [Ge] 0  and a same thickness. 
     
     
       8. The method according to  claim 1 , wherein the second diffusion takes place in a neutral or non-oxidizing atmosphere. 
     
     
       9. The method according to  claim 1 , wherein the second diffusion is configured in time and temperature such that a diffusion distance d of the germanium in the second direction x is between 10 nm and 30 nm. 
     
     
       10. The method according to  claim 1 , wherein the second diffusion is carried out at a temperature T 2  between 950° C. and 1,150° C., for a time t 2  between 5 s and 60 s. 
     
     
       11. The method according to  claim 1 , wherein the second diffusion is carried out under similar conditions to that of the first diffusion, such that the second diffusion forms a continuation of the first diffusion. 
     
     
       12. The method according to  claim 1 ,
 further comprising forming first and second gates on the first and the second SiGe-based portions, respectively, 
 the first and the second gates having first and second gate lengths Lg 1  and Lg 2 , respectively, and 
 the first and the second Ge concentrations [Ge] 1  and [Ge] 2  and the gate lengths Lg 1  and Lg 2  being such that the first and the second gates have an identical threshold voltage Vth. 
 
     
     
       13. An electronic device, comprising:
 a substrate comprising a silicon-based layer, the silicon-based layer comprising at least a first SiGe-based portion having a first Ge concentration [Ge] 1 , and at least a second SiGe-based portion having a second Ge concentration [Ge] 2  that is lower than [Ge] 1 , the first and the second portions being formed by the method according to  claim 1 ; and 
 first and second gates on the first and the second SiGe-based portions, respectively, the first and the second gates having first and second gate lengths Lg 1  and Lg 2 , respectively, the first and the second Ge concentrations [Ge] 1  and [Ge] 2  and the gate lengths Lg 1  and Lg 2  being such that the first and the second gates have an identical threshold voltage Vth.